**10.2 Biogas production from grasses and wild plants**

A study by Sidibe and Hashimoto (1990) documented the fact that grass straw can be fermented to methane and the yield can be relatively high. This laboratory experiment showed that the ultimate methane yield of rye grass straw (341+ 5ml/g VS) and fescue grass

Potentials of Selected Tropical Crops and Manure as Sources of Biofuels 23

Methane (65.0%), CO2 (34.94%). WH-A contained Methane (60.0%), CO2 (39.94%). WH-T contained Methane (71.0%), CO2 (28.94%), while WH-C had Methane (64.0%) CO2 (35.94%). The other gases were found in the same levels and in trace amounts in all the systems. The overall results showed that treating water Hyacinth with KOH did not have a significant improvement on the biogas yield. It also indicated that water Hyacinth is a very good biogas

As pointed out by Barber et al., (2010) perennial grasses benefit the environment in numerous ways. They help to reduce climate change, increase energy efficiency and will constitute a sustainable energy resource for the world. Switchgrass, the most widely used perennial grass for biofuels, is also in such a manner, beneficial to both farmers as well as energy consumers in general. Perennial grasses are crucial to the ecosystem to create a sustainable energy resource for the world and also to limit the use of fossil fuels. These grasses are important because they can produce ethanol, an energy source that emits much less carbon dioxide than other fossil fuels. Reducing carbon dioxide emissions is important because carbon dioxide emissions in the atmosphere constitute one of the leading causes of climate change. Barry (2008) pointed out that 1 bale of switchgrass can yield up to about 50 gallons of ethanol. As reported by Rinehart (2006), researchers are using switchgrass as a biofuel so that they can successfully reduce carbon dioxide emissions. Switchgrass has a high energy in and out ratio because of lignin, the byproduct of the cellulose conversion that stores internal energy for its energy transformation process. Ethanol reduces carbon dioxide emissions by approximately ninety percent when compared to gasoline and consequently, carbon dioxide in the ozone layer of our atmosphere will slowly begin to deplete itself as biofuels created from switchgrass, other grasses and other ethanol sources are utilized. As a rule, all species of the grass family (poaceae) contain starch and should be able to yield

Manure has for a long time been recognised as a renewable source of energy. Earlier practices involved direct combustion of manure to produce heat energy; while latter practices involved gasification of manure, followed by combustion. The more recent practices involved anaerobic biodigestion of manure to produce biogas which is scrubbed to

Huge quantities of manure are produced on farms. In fact a cattle farming operation which has a herd size of 10,000 animals can on a daily basis generate wastes equal to that produced by a city of half a million residents. Considering cattle for instance reported values of daily manure production range from 10kg (VITA, 1980) to 60kg (Safley Jr, et al., 1985) per animal. Legg (1990) reports that the 8.5, 28, 6.9 and 104 million cattle, sheep, pigs and poultry reared in England and Wales produced 80, 11, 11, and 30 million tonnes of manure respectively for the year immediately preceding. Smith and Chambers (1998) noted that manure arising from dairy beef farming comprise the majority (73 million tonnes) of the 90 million tonnes

producer and the yield can be improved by drying and combining it with cow dung.

**10.3 Ethanol production from common grasses** 

ethanol.

**11. Manure as a biofuel** 

purer methane and then combusted.

**11.1 On-farm availability of manure** 

straw (356+ml/g VS) are not significantly different but both grass straws had significantly higher yield (p < 0.01) than dairy cattle manure (288 + 3 ml/g VS). The paper noted that nitrogen does not appear to be a limiting nutrient in the fermentation of grass straw to methane; the length of time between inocula feeding does not affect the ultimate methane yield of the straw, and longer acclimation may increase the ultimate methane yield of grass straw. Among plants themselves, differences exist regarding their potentials as feedstock for biogas production. For instance, De–Renzo (1997) reviewed anaerobic digestion of plant materials and concluded that aquatic plants such as algae and moss can be much better digested than terrestrial plants because of their toughness. Ordinarily, more digestion results in more biogas production. Akinbami et al (2001) noted that in the tropics, the identified feedstock substrates for an economically feasible biogas programme include water lettuce, water hyacinth, dung, cassava peelings, cassava leaves, urban refuse, solids (including industrial waste), agricultural residue and sewage.

Uzodinma and Ofoefule (2009) investigated the production of biogas from equal blending of field grass (F-G) with some animal wastes which include cow dung (G-C), poultry dung (G-P), swine dung (G-S) and rabbit dung (G-R). The wastes were fed into prototype metallic biodigesters of 50 L working volume on a batch basis for 30 days. They were operated at ambient temperature range of 26 to 32.8oC and prevailing atmospheric pressure conditions. Digester performance indicated that mean flammable biogas yield from the grass alone system was 2.46±2.28 L/total mass of slurry while the grass blended with rabbit dung, cow dung, swine dung and poultry dung gave average yield of 7.73±2.86, 7.53±3.84, 5.66±3.77 and 5.07±3.45 L/total mass of slurry of gas, respectively. The flash point of each of the systems took place at different times. The field grass alone became flammable after 21 days. The grass-swine (G-S) blend started producing flammable biogas on the 10th day, grass-cow (GC) and grass-poultry (G-P) blends after seven (7) days whereas grass-rabbit (G-R) blend sparked on the 6th day of the digestion period. The gross results showed fastest onset of gas flammability from the G-R followed by the G-C blends, while the highest average volume of gas production from G-R blend was 3 times higher than that of F-G alone. Overall, the results indicated that the biogas yield and onset of gas flammability of field grass can be significantly enhanced when combined with rabbit and cow dung.

Ofuefule et al., (2009) reported a comparative study of the effect of different pre-treatment methods on the biogas yield from Water Hyacinth (WH). The WH charged into metallic prototype digesters of 121 L capacity were pre-treated as: dried and chopped alone (WH-A), dried and treated with KOH (WH-T), dried and combined with cow dung (WH-C), while the fresh water Hyacinth (WH-F) served as control. They were all subjected to anaerobic digestion to produce biogas for a 32 day retention period within a mesophilic temperature range of 25 to 36°C. The results of the study showed highest cumulative biogas yield from the WH-C with yield of 356.3 L/Total mass of slurry (TMS) while the WH-T had the shortest onset of gas flammability of 6 days. The mean biogas yield of the fresh Water Hyacinth (WH-F) was 8.48 ± 3.77 L/TMS. When the water Hyacinth was dried and chopped alone (WH-A), dried and treated with KOH (50% w/v) (WH-T) and dried and combined with cow dung (WH-C), the mean biogas yield increased to 9.75 ± 3.40 L/TMS, 9.51 ± 5.01 L/TMS and 11.88 ± L/TMS respectively. Flammable biogas was produced by the WH-F from the 10th day of the digestion period whereas the WH-A, WH-T and WH-C commenced flammable gas production from the 9th, 6th and 11th day respectively. Gas analysis from WH-F shows Methane (65.0%), CO2 (34.94%). WH-A contained Methane (60.0%), CO2 (39.94%). WH-T contained Methane (71.0%), CO2 (28.94%), while WH-C had Methane (64.0%) CO2 (35.94%). The other gases were found in the same levels and in trace amounts in all the systems. The overall results showed that treating water Hyacinth with KOH did not have a significant improvement on the biogas yield. It also indicated that water Hyacinth is a very good biogas producer and the yield can be improved by drying and combining it with cow dung.
